The present invention relates to a plasma display panel, in particular to a surface discharge type plasma display panel.
Recently, there has been a demand that a surface discharge type plasma display panel be put into actual use, i.e., for use as a color display device which is large in size but small in thickness. FIG. 10 is a plane view schematically illustrating the structure of a conventional surface discharge type plasma display panel. FIG. 11 is a cross sectional view, taken along line V--V in FIG. 10, schematically indicating the internal structure of the plasma display panel of FIG. 10.
Referring to FIG. 10, the conventional plasma display panel has a plurality of row electrode pairs 2,2, each arranged along a display line L of a matrix array on the panel, in a manner such that each electrode pair 2,2 has a discharge gap 11 formed therebetween. Further, along each display line L, there are formed several unit luminescent areas, each of which forms a picture element cell (discharge sell).
FIG. 11 is used to illustrate some important portions of the conventional display panel of FIG. 10. As shown in FIGS. 10 and 11, formed on the inner surface of a front glass substrate 1 (serving as a front display plate), are a plurality of strap-like inorganic pigment layers 41 forming color filter layers corresponding to a plurality of elongated fluorescent layers 7 involving various colors, a transparent overcoat 42 covering the inorganic pigment layers 41, a plurality of row electrode pairs 2,2, a dielectric layer 3 covering the row electrode pairs 2,2, a protection layer 4 consisting of MgO covering the dielectric layer 3.
Each row electrode 2 includes a transparent electrode 2a consisting of a strap-like transparent conductive film of ITO having a relatively large width, and a metal electrode (bus electrode) 2b consisting of a metal film having a relatively small width. The metal electrode 2b is used to supplement the conductivity of the transparent electrode 2a.
On the other hand, a rear glass substrate 5 is positioned spaced apart from the front glass substrate 1 so that a discharge space 8 is formed between the two substrates. As shown in FIG. 11, a plurality of column electrodes 6 are provided on the inner surface of the rear glass substrate 5 in a manner such that they are all orthogonal to the row electrode pairs 2,2. In fact, intersections of the row electrode pairs 2,2 with the column electrodes 6 form picture element cells. Further, a plurality of strap-like partitions 9 are provided between the column electrodes 6, so that the discharge space 8 is divided into several sections. Inaddition, a plurality of elongated fluorescent layers 7 are disposed in the discharge space 8 to cover the column electrodes 6 and side walls of the partitions 9. Finally, after a noble gas is sealed into the discharge space 8, a desired surface discharge type plasma display panel is thus formed.
In use of the surface discharge type plasma display panel constructed in the above prior art, at first, an addressing process is conducted by selective discharge between the column electrodes 6 and the row electrodes 2, so as to select lighting cells (in which wall charges are formed) and not-lighting cells (in which wall charges are not formed). After the addressing process, by alternatively applying discharge maintaining pulses to the row electrode pairs 2,2 on all the display lines L, a surface discharge will occur every time the discharge maintaining pulses are applied to the lighting cells. Then, with the effect of the surface discharge, an ultraviolet light will occur, so that the fluorescent layer 7 will be excited, thereby producing a visible light.
Conventionally, in order to improve a contrast and a color fineness of a surface discharge type plasma display panel, a plurality of strap-like inorganic pigment layers 41 forming color filter layers are usually provided on the inner surface of the front glass substrate 1. As a method for forming the inorganic pigment layers 41, it has been suggested that such inorganic pigment layers 41 be formed on the inner surface of the front glass substrate 1 by way of screen printing. With the use of this method, since the color filter layers 41 may be made into a small thickness having only several microns, it is allowed to reduce surface irregularities possibly caused by the color filter layers.
However, since the strap-like inorganic pigment layers 41 are only attached on to the inner surface of the front glass substrate 1, they are likely to peel off during a process when the row electrodes 2 are being formed with the use of a photolithograph method. In order to cope with such problem, there has been suggested another method in which an amount of low melting point glass paste is applied to the surfaces of strap-like inorganic pigment layers 41 and also applied to the exposed surface areas on the inner surface of the front glass substrate 1, followed by a baking treatment, so as to form an overcoat layer 42 consisting of a transparent material which is useful to firmly fix the inorganic pigment layers 41 on the inner surface of the front glass substrate 1.
But, one problem with the above second method is that it is difficult for the overcoat layer material to sufficiently penetrate into and through the inorganic pigment layers 41, and another problem is that since the inorganic pigment layers 41 are disposed between the front glass substrate 1 and the overcoat layer 42, the effective areas (between the strap-like inorganic pigment layers 41) useful for bonding the overcoat layer 42 with the front glass substrate 1 are not enough. As a result, it is likely that some defects such as pin holes and/or cracks will occur on the overcoat layer 42, causing the overcoat layer 42 to peel off, resulting in a problem that during a photolithograph process for forming row electrodes 2, a treatment liquid will invade into the inorganic pigment layers 41, causing undesired color change thereon. In addition, since the effective areas (between the strap-like pigment layers 41) useful for bonding the overcoat layer 42 with the front glass substrate 1 are only narrow strap-like areas, the overcoat layer 42 has only a weak strength that is difficult to resist a possible stress. On the other hand, if the thickness of the overcoat layer 42 is increased in order to avoid the above problem, the overcoat layer 42 with a large thickness will have only a low light transmissivity. Moreover, if there are some deflections among strap-like inorganic pigment layers 41, the effective areas useful for bonding the overcoat layer 42 with the front glass substrate 1 will be reduced somehow, resulting a weak adherence between these two members.
FIGS. 12-14 are views schematically illustrating the structure of another conventional surface discharge type plasma display panel.
As shown in FIG. 12 which is a plane view, a plurality of row electrode pairs 2,2 are provided and arranged in a manner such that each pair forms a discharge gap G on each display line L. Along each display lineL, there are formed several unit luminescent areas each serving as a picture element cell (discharge sell), at intersections where the row electrodes 2 are intersected with column electrodes (not shown in FIG. 12).
FIG. 13 is a cross sectional view taken along line V--V in FIG. 12, schematically indicating the internal structure of the plasma display panel of FIG. 12. In fact, formed on the inner surface of a front glass substrate 1 (serving as a front display plate), are a plurality of strap-like inorganic pigment layers 41 (41R, 41G, 41B) forming color filter layers corresponding to a plurality of elongated fluorescent layers 7 (FIG. 14) involving various colors, a transparent overcoat 42 covering the inorganic pigment layers 41, a plurality of row electrode pairs 2,2, a dielectric layer 3 covering the row electrode pairs 2, 2, a protection layer 4 consisting of MgO for covering the dielectric layer 3.
Each row electrode 2 includes a transparent electrode 2a consisting of a strap-like transparent conductive film of ITO having a relatively large width, and a metal electrode (bus electrode) 2b consisting of a metal film having a relatively small width. The metal electrode 2b is used to supplement the conductivity of the transparent electrode 2a.
On the other hand, a rear glass substrate 5 is positioned spaced apart from the front glass substrate 1 so that a discharge space 8 is formed between the two substrates. As shown in FIG. 13, a plurality of column electrodes 6 are provided on the inner surface of the rear glass substrate 5 in a manner such that they are all orthogonal to the row electrode pairs 2,2. In fact, intersections of the row electrode pairs 2,2 with the column electrodes 6 form picture element cells. Further, a plurality of strap-like partitions 9 are provided between the column electrodes 6, so that the discharge space 8 is divided into several sections. Inaddition, a plurality of elongated fluorescent layers 7 are disposed in the discharge space 8 to cover the column electrode 6 and side walls of the partitions 9. Finally, after noble gas is sealed into the discharge space 8, a plasma display panel is thus formed.
In use of the surface discharge type plasma display panel constructed as shown in FIGS. 12-14, at first, an addressing process is conducted by selective discharges between the column electrodes 6 and the row electrodes 2, so as to select lighting cells (in which wall charges are formed) and not-lighting cells (in which wall charges are not formed). After the addressing process, by alternatively applying discharge maintaining pulses to the row electrode pairs 2,2 on all the display lines L, a surface discharge will occur every time the discharge maintaining pulses are applied to the lighting cells. Then, with the effect of the surface discharge, an ultraviolet light will occur, so that the elongated fluorescent layers 7 are excited, thereby producing a visible light.
Conventionally, in order to improve a contrast and a color fineness of a surface discharge type plasma display panel, a plurality of strap-like inorganic pigment layers 41R, 41G, 41B are usually provided on the inner surface of the front glass substrate 1 by virtue of screen printing.
However, if several inorganic pigment layers 41R, 41G, 41B are disposed on the inner surface of a front glass substrate 1, these color filters 41 are difficult to be made uniform in their thickness, because different color filter layers are usually manufactured with different requirements and have different optical characteristics. Moreover, as shown in FIG. 14, since the pigment layers 41R, 41G, 41B are formed into strap-like shape, there are formed some convex and concave portions (irregularities) on the surface of the protection layer 4. To eliminate such irregularities, an overcoat layer 42 is often formed to cover up these pigment layers 41, but still fails to obtain a smooth and flat surface, unavoidably producing some convex-concave portions of several microns.
On the other hand, if the metal layers forming the metal electrodes 2b are made of a silver paste forming into a coating layer having a thickness of several micron, there will also form some convex and concave portions (irregularities) on the surface of the protection layer 4, as shown in FIG. 13. As a result, some undesired gaps will be undesirably formed between the partition walls 9 and the protection layers 4, resulting in a problem that a discharge in one cell will undesirably spread to an adjacent cell through such gaps, hence causing a wrong discharge.